Stress mitigating and growth enhancing effect of dietary tryptophan in rohu (Labeo rohita, Hamilton, 1822) fingerlings.

An experiment was conducted to study the stress mitigation and growth enhancing role of dietary L-tryptophan (TRP) under thermal stress in rohu, Labeo rohita fingerlings for 45 days. Seven hundred and twenty fishes were distributed in three major groups that are ambient temperature (26 °C), 34 and 38 °C in triplicate following a complete randomized design. Acclimation of fishes to 34 and 38 °C over average ambient temperatures were carried out at 1 °C/day. Each group was fed with a diet supplemented with 0, 0.36, 0.72 or 1.42 % L-TRP. Results showed that blood glucose and serum cortisol level were found to be significantly higher (p < 0.05) in the higher temperature groups than the ambient temperature group. Similarly, aminotransferase, lactate dehydrogenase, malate dehydrogenase, CAT, superoxide dismutase activities were found to be significantly higher (p < 0.05) in the control groups (0 % L-TRP) and decreasing activities of these enzymes were observed with the increasing level of dietary L-TRP. In different temperature groups, L-TRP-supplemented groups were found to have higher (p < 0.05) growth, RGR and PER. The results obtained in the present study indicate that dietary L-TRP mitigates thermal stress and enhances growth. From the present study, we can conclude that dietary supplementation of L-TRP at the 0.72 % level in the diet is found to be optimum to reduce thermal stress even up to 38 °C in rohu, L. rohita. The baseline data obtained here could be useful for the farmers to formulate feeds to culture the fish in different agro-climatic zones.

Expression of immune-related genes in rohu Labeo rohita (Hamilton) by experimental freshwater lice Argulus siamensis (Wilson) infection.

The crustacean ectoparasite, Argulus poses one of the major threats to carp culture due to absence of any suitable control measure. The study was undertaken to determine the expression of immune-related genes in three major immunocompetent organs viz., kidney, skin and liver of rohu (Labeo rohita) during experimental freshwater lice Argulus siamensis infection. Results showed that the expression of TLR 22-like, lysozyme G and ß2-microglobulin genes in kidney was significantly (P ≤ 0.05) down-regulated in lice-infected fish. On the other hand, no significant difference (P>0.05) in CXCa, lysozyme C, TNFα and complement component 3 (C3) expression was found between uninfected control and different degrees of lice infected fish. In the skin, the expression of TLR 22-like and TNFα genes were significantly up-regulated whereas that of C3 was significantly (P ≤ 0.05) down-regulated in lice-infected fish with respect to control fish. The expression of CXCa, lysozyme C and transferrin was not detected in the skin samples of fish. In the liver, the expression of CXCa, lysozyme G, ß2-microglobulin and transferrin was significantly (P≤0.05) up-regulated in lice-infected fish with respect to control fish whereas expression of C3 was significantly (P ≤ 0.05) down-regulated in lice-infected fish. The expression of TLR 22-like, lysozyme C, TNFα genes was not detected in the liver samples of fish. This study indicates that majority of the genes showed down-regulation in kidney tissue whereas up-regulation in liver and skin tissues except C3 in Argulus-infected fish. We show that infection with this parasite irrespective of intensity can also result in immune gene expression changes in tissues situated away from the site of parasite attachment and feeding. The information obtained here could be useful towards understanding the susceptibility of rohu to argulosis and mechanisms involved in protection of rohu to ectoparasitic infections, which is causing immense economic losses to freshwater aquaculture sector.